Digital signal processors (DSPs) are computing devices that process data that has been converted from analog form to digital form. Among the functions typically performed by DSPs are compression and decompression of data and echo cancellation. In traditional applications, one DSP has typically been placed on one integrated circuit chip. Several advantages can be gained by placing multiple DSPs on a single chip rather than having only one DSP on a chip. First, the amount of space on a circuit board taken up by the DSPs is reduced. Under the traditional approach, if four DSPs were needed in a circuit, four separate chips would have to be placed on the circuit board. When four DSPs are placed on a single chip, only one chip is needed instead of four and the amount of space on the circuit board used by the DSPs is reduced accordingly. Electrical energy tends to be wasted by the random access memory, input/output, and other peripherals on each chip and particularly by the input/output ports. The use of a multi-DSP chip reduces this waste by reducing the number of chips on the board. Connections between the multiple DSPs on one chip do not need input/output circuits, but instead operate at the low internal power levels. Thus, the amount of power consumed by the circuit board and the amount of heat generated by the board are reduced. The reductions in space and energy consumption contribute to a cost savings for multi-DSP as opposed to single-DSP chips. The use of multiple DSPs on a single chip instead of on separate chips also increases processing speed by reducing the distance between the DSPs and decreasing the number of interconnections among them.
Prior to the development of the present invention, at least one chip was known to exist that improved on the traditional configuration by placing multiple DSPs on a single chip. The Texas Instruments TMS320VC5441 Fixed-Point Digital Signal Processor contains four DSPs in a single integrated circuit. The TMS320VC5441 is described in a Texas Instruments data manual, Literature Number SPRS122C, which is incorporated herein by reference.
While the Texas Instruments TMS320VC5441 offers the advantages described above, that chip also has several drawbacks. Communication between each DSP and a host processor outside the chip is achieved through a multiplexing unit connected to a host processor interface on each DSP subsystem. Because of the multiplexing function, only one DSP can be accessed at a time, slowing down overall communication speed within the chip. The presence of a host processor interface on each DSP subsystem adds to the complexity of the chip and increases the number of interconnections needed among the components on the chip. Also, the host processor interface on each DSP subsystem shares a data bus with a memory control unit. Because of this configuration, memory access speed is reduced when the host processor interface is active. The present invention overcomes these drawbacks while retaining the advantages previously described.